Cell death is a normal component of development and functioning of multicellular organisms. Being a natural process, cell death is involved in the pathology of numerous diseases caused by internal factors. Cell death also accompanies diseases caused by external physical, chemical, of biological agents.
There exist two major types of cell death, necrosis and apoptosis, marked by different morphological and molecular characteristics (Kerr et al., Br. J. Cancer. 26, 239-257 (1972); Umansky, Theor. Biol. 97, 591-602 (1982); Umansky et al., Adv Pharmacol. 41, 383-407 (1997); Ameisen, Cell Death Differ. 11, 4-10 (2004); Lockshin et al. Int J Biochem Cell Biol. 36, 2405-19 (2004); G. Kroemer, et al., Cell Death and Differentiation 12, 1463-1467 (2005)). Necrosis is considered to be catastrophic metabolic failure resulting directly from severe molecular and/or structural damage and leads to inflammation and secondary damage to surrounding cells. Apoptosis is a much more prevalent biological phenomenon than necrosis and can be induced by specific signals such as hormones, cytokines, by absence of specific signal such as growth or adhesion factors, or by molecular damage that does not cause catastrophic loss of integrity. Apoptosis is a result of an active cellular response involving initiation of an orderly and specific cascade of molecular events. Apoptosis leads to the appearance of distinctive chromatin condensation and margination, nuclear fragmentation, cell shrinkage, membrane blebbing and enzymatic internucleosomal fragmentation of nuclear DNA (Umansky et al., Biochim Biophys Acta. 655, 9-17 (1981); Arends et al., Am J. Pathol. 136, 593-608 (1990)). Other more rare forms of cell death, characterized by specific morphology, for example, so called autophagic cell death have also been described (Bredesen et al., Stroke. 38(2 Suppl):652-660 (2007).
Independent of a specific mechanism and type of cell death, methods to detect dying cell types are important for diagnosis of various diseases, critical for disease and treatment monitoring, and helpful for differential diagnosis. Besides, the methods capable of detection of specific cell death in vivo are useful for developing drugs aiming at prevention or induction of cell death as well as for analysis of the cytotoxicity of the newly developed drugs.
There are some clinical tests for diagnosis of disease-related excessive cell death based on detection of tissue specific markers, such as for example antigens, enzymes and other proteins in blood or in other bodily fluids. Measurement of the activity of liver-specific enzymes in blood, for example, is a widely used method for evaluation of hepatocyte death (Amacher, et al., Regul Toxicol Pharmacol. April; 27(2):119-130 (1988); Salaspuro, et al., Enzyme. 37:87-107 (1987); Herlong, Hosp. Pract. (Off Ed).29(11):32-38 (1994)). Evaluation of the level of cardiomyocyte specific antigens has also been used for diagnosis of the myocardial infarction (Mair et al., Clin Chem Lab Med. 37:1077-1084 (1999); Nunes et al., Rev Port Cardiol. 20:785-788 (2001)). However, the number of such techniques is limited to diseases in which a marker and a method of detection are known in order for the analysis to provide meaningful, tissue-specific results (Oh S et al., Curr Gastroenterol Rep. 3:12-18 (2001); Rochling et al., Clin Cornerstone. 3(6):1-12 (2001)). Other methods require invasive biopsy of specific tissues suspected of having a diseased condition to get a specimen for analysis. However, biopsy of some organs and tissues, for example brain is highly invasive and often difficult to perform.
It is well known that apoptosis, or programmed cell death, which is a major form of cell death in the mammalian organism, is accompanied by internucleosomal fragmentation of nuclear DNA. Many laboratories have demonstrated that a portion of this DNA appears in blood (Lo Y. M. Ann NY Acad Sci. 945:1-7 (2001); Lichtenstein et al., Ann N Y Acad Sci. 945:239-249 (2001); Taback et al., Curr Opin Mol Ther. 6:273-278 (2004); Bischoff et al., Hum Reprod Update. 8:493-500, (2002)). It has also been shown that this fragmented DNA, called transrenal DNA (Tr-DNA) crosses the kidney barrier and can be detected in the urine (Botezatu et al., Clin Chem. 46:1078-1084, (2000); Su et al., J Mol Diagn. 6:101-107 (2004); Su et al., Ann N Y Acad Sci. 1022:81-89 (2004).
Although both cell-free plasma DNA and Tr-DNA may be used as diagnostic tools, they provide a rather limited approach when evaluating tissue specific events, such as cell death. Thus analytical methods that are non-invasive, and provide a broader range of indications of specific pathology, due to their ability to detect levels of dying cells in particular tissues and organs, would be useful for diagnosing and monitoring the state of various diseases or pathological conditions in patients. In addition, tissue specific analytical methods that provide the means for monitoring the response of a patient to a disease therapy would be useful to determine the therapy effectiveness, and in the case of drug treatment, the optimum dosage required for drug administration.
To address these problems, the instant invention is focused on the use of micro RNA (miRNA) as a diagnostic tool to monitor in vivo cell death in bodily fluids, such as for example serum and urine. Unlike cell-free plasma DNA and Tr-DNA, many miRNAs exhibit cell, tissue and organ specific expression profiles (Liang et al., Genomics, 8:166 (2007); Lukiw et al, Neuroreport. 18:297-300 (2007); Lagos-Quintana et al., Curr Biol. 12:735-739 (2002); Chen et al., Nat Genet. 38:228-233 (2006); Beuvink et al., J. Nucleic Acids Res. 35:e52 (2007)). Furthermore, correlation of miRNA cell and tissue specific profiles with different pathologies and tumor types have been demonstrated (Visone R., et al. Oncogene. 26:7590-7595 (2007); Nelson et al., Neuropathol Exp Neurol. 66:461-468 (2007); Negrini et al., J Cell Sci. 120:1833-1840 (2007); Chang et al., Annu Rev Genomics Hum Genet. 8:215-239 (2007); Jay et al., Cell Biol. 26:293-300 (2007)).
Thus, the instant invention provides methods for measuring in vivo cell death by detection of tissue-specific miRNAs, characteristic of a specific pathology, in body fluids, such as for example serum and urine. The instant methods based on detection of miRNAs in bodily fluids are used for further development of diagnostic or monitoring tests.